The present invention relates to devices and methods pertaining to telecommunications equipment, and more particularly to methods for coupling TDM-channels through a node in a telecommunications system. The invention also relates to such nodes, and to a device board in such a node, and to a telecommunications system that includes such device boards and such nodes.
Several different ways of coupling TDM-channels through a node with the aid of different forms of transport modules, such as cells for instance, are known in the art.
U.S. Pat. No. 5,237,564 describes how frames are coupled through an ATM-switch, said frames being referred to as frame relay types and having variable lengths.
U.S. Pat. No. 5,412,655 describes a system which couples TDM-channels through an ATM-switch. In this system, there is received a frame which includes a plurality of time slots of which each may include a TDM-channel. Information transmitted in the channels is stored in a corresponding buffer, i.e. there is one buffer for each TDM-channel. When one such buffer is full, its contents are sent through the switch in an ATM-cell and one cell is thus used with each connection.
U.S. Pat. No. 5,450,411 describes a system for multiplexing isochronous data and burst data and sending the multiplexed data through an ATM-switch with the aid of an ATM-cell.
WO94/11975 and WO95/17789 describe ATM-networks. Among other things, these documents describe an ATM node or an ATM-switch which receives traffic in the form of PCM signals (Pulse Code Modulation) in channels having the form of time slots in mutually sequential frames, wherein PCM signals arriving at ATMU units (ATM Interface Unit) are packed in ATM-cells and coupled through an ATM-switch core to a corresponding ATMU unit, where the PCM signals are transmitted in time slots in mutually sequential frames. A node or switch contains several such ATMU units and all PCM channels that are to be transmitted between two such ATMU units are packed in the same cell. An ATMU unit receives the PCM signals on something that is referred to as NCT links, and includes a number of multiplexors coupled to a matrix-configured buffer CWB (Cell Wide Buffer) which is dimensioned in accordance with the number of bytes (i.e. the complete PCM word in a time slot) that can be included in an ATM-cell, and also in accordance with the number of other ATMU units present in the node. In this case, the number of multiplexors is equally as large as the number of bytes that can be accommodated in a cell. All multiplexors are also connected to an incoming NCT line. These multiplexors receive mutually synchronized frames with time slots over the NCT lines, and each multiplexor is able to switch a selected time slot from a selected line to a selected position in CWB. In this case, the multiplexors first switch the first time slot of all incoming frames to selected positions, and then switch the second time slot of all frames, and so on. Cells are then formed from the contents of the CWB. ATMU operates essentially in the same way in the opposite direction, although with the use of demultiplexors which couple out bytes with PCM signals on NCT lines synchronously with one another. In this case, the multiplexors and demultiplexors operate synchronously with one another and thus require all channels to be equally large for switching the channels. The size described is that of pulse-code modulated signals, which normally have a size of one byte. However, channels of different sizes on one and the same line are very usual in the concept of present-day telecommunications. For instance, it is usual to compress PCM signals and take up less than one byte, for instance. Such compression may be of interest when wishing to reduce the costs of using a public network. The aforedescribed system does not allow such smaller channels to be switched at the same time as switching the larger PCM channels, because of the use of multiplexors. The system described in this prior publication also requires the NCT lines, as experienced by the multiplexors, to be synchronized with one another.
The present invention addresses the problem of how TDM-channels of mutually different sizes can be coupled simultaneously through a node in a telecommunications system when all TDM-channels that are received in a frame on a device board in the node and that shall be sent to a second device board in the node are packed in a common transport module.
This problem is solved by storing in an input buffer the contents of a frame from an information stream received on a first device board, copying the contents of all TDM-channels that are stored in each such input buffer on the first device board and that are to be further coupled from the node via a transmitting section of a second device board, to a transmitting buffer corresponding to said transmitting section, and sending the content of the transmitting buffer to the second device board by means of a transport module.
The problem is also solved by receiving one such transport module that includes TDM-channels in a transmitting section of a second device board in the node, wherein the transport module solely includes a plurality of TDM-channels arriving from a first device board, wherein the content of the transport module is stored in a receiving buffer corresponding to the first device board, wherein all TDM-channels in each receiving buffer on the second device board that shall be sent in a frame on a node outgoing line are copied in an output buffer to positions corresponding to said channels, and wherein the content of the output buffer is sent in a frame in a node-outgoing information stream that includes mutually sequential frames.
Thus, an object of the present invention is to provide a method, a telecommunications system, a node, and a device board in which simultaneous coupling of TDM-channels of mutually different sizes through a node in a telecommunications system is achieved wherewith all TDM-channels that are received in a frame on a device board in the node and that shall be sent to a second device board in said node are packed in a common transport module which is sent to said second device board.
The object is achieved with a method that includes the steps of receiving in a receiving section of a first device board in the node at least one information stream that includes mutually sequential frames, where each frame includes a number of TDM-channels, storing the content of one frame from an information stream in a corresponding input buffer, copying the content of all TDM-channels that are stored in each such input buffer and that are to be forwarded from the node to a second device board via a transmitting section (27) to at least one transmitting buffer corresponding to said transmitting section, and transmitting the content of the transmitting buffer by means of at least one transport module.
The object is also achieved with a telecommunications system, a node in a telecommunications system, and a device board in such a node, wherein the device board includes a receiving section that has at least one input port for receiving. TDM-channels in TDM-frames, and at least one transmitting buffer which is adapted for connection between the receiving section and a transmitting section of another device board. Each input port has connected thereto at least one corresponding input buffer for receiving a frame that contains TDM-channels, wherein each input buffer is also connected to each transmitting buffer. The receiving section also includes control means. The control means is connected to all transmitting buffers and to all input buffers and is responsible for copying to said transmitting buffer all the TDM-channels that are received on the device board and stored in the input buffers and that are intended for the transmitting section of the other device board, and to ensure that the content of the transmitting buffer reaches the transmitting section of the other device board, by sending at least one transport module that contains solely all TDM-channels that are intended for the other device board.
The object is also achieved with a method comprising the steps of receiving at least one transport module including TDM-channels in a transmitting section of a second device board in the node, wherein the transport module contains solely a number of TDM-channels arriving from a first device board, storing the content of the transport module in a receiving buffer corresponding to the first device board; copying on the second device board all TDM-channels in each receiving buffer that shall be sent in a frame on a node-outgoing line to positions in an output buffer corresponding to said channels, and sending the content of the output buffer in a frame in a node-outgoing information stream that includes mutually sequential frames.
The object is also achieved with a telecommunications system, a node in a telecommunications system, and a device board in such a node, wherein the device board includes a transmitting section having at least one output port and at least one receiving buffer for storing all TDM-channels that have been received from at least one other device board through the medium of at least one transport module, wherein a transport module contains solely TDM-channels from another device board. Each output port has at least one output buffer connected thereto, wherein each output buffer is also connected to each receiving buffer. The transmitting section also includes control means connected to each output buffer and to each receiving buffer. The control means causes storage of the content of a transport module received from another device board in a corresponding receiving buffer, copying from each receiving buffer all TDM-channels that are to be sent in a frame from an output port to positions in a corresponding output buffer corresponding to said channels, so as to enable the TDM-channels to be sent from the transmitting section in a frame in a node-outgoing information stream that includes mutually sequential TDM-frames.
The invention also solves another problem of through-coupling TDM-channels where information streams containing line-carried TDM-channels arrive at and leave from a node without being synchronized with one another.
This other problem is solved by receiving a number of TDM-channels in a receiving section of a first device board in the node via at least two different input ports, and sending all TDM-channels that shall be forwarded from the node via a transmitting section of a second device board to said transmitting section by means of at least one transport module first when each input port has received its respective frame, said transport module containing solely all of the TDM-channels intended for said other device board.
The second problem is also solved by receiving in the transmitting section of a second device board transport modules that include TDM-channels, unpacking the TDM-channels from the transport modules, and then forwarding all TDM-channels that have been obtained in this way in at least one TDM-frame, wherein TDM-channels that have been received in the transmitting section are forwarded in frames via at least two output ports, and a frame is forwarded from a port only when all TDM-channels to be sent in said frame have been received in the transmitting section.
Thus, it is also an object of the invention to provide a method, a telecommunications system, a node and a device board for through-coupling TDM-channels when information streams including TDM-channels that arrive at and leave from said node on lines are not synchronized with one another.
This object is achieved with a method in which frames that include a number of TDM-channels are received in a receiving section of a first device board in the node via at least two different input ports; and in which all TDM-channels that are to be forwarded from the node via a transmitting section of a second device board are sent to said transmitting section by means of at least one transport module, said transport module containing solely all of the TDM-channels that are intended for the second device board. All transport modules are sent from the receiving section only when each input port has received its respective frame.
The object is also achieved with a telecommunications system, a node in a telecommunications system, and a device board in such a node, wherein the device board includes a receiving section which has at least two input ports for receiving TDM-channels in TDM-frames, at least one transmitting buffer which is adapted for connection between the receiving section and a transmitting section of another device board, and a control means which is connected to the transmitting buffer and adapted, on the one hand, to store therein all those TDM-channels received on the device board that are intended for the transmitting section of the other device board, and, on the other hand, to ensure that the content of the transmitting buffer reaches the transmitting section of the other device board, by sending at least one transport module which contains solely all TDM-channels intended for said other device board, wherein transmission of all transport modules from the receiving section takes place only when each input port has received its respective frame.
The object is also achieved with a method in which transport modules are received in the transmitting section (27) of a second device board, wherein the transport modules include TDM-channels that have been coupled through the node from a second device board, wherein the TDM-channels are unpacked from the transport modules, wherein all TDM-channels obtained in this way are then forwarded in TDM-frames via at least two output ports, and wherein a frame is forwarded from a port when all TDM-channels to be sent in this frame have been received in the transmitting section.
The object is also achieved with a telecommunications system, a node in a telecommunications system and a device board in such a node, wherein the device board includes a transmitting section having at least one output port, at least one receiving buffer for storing all TDM-channels that have been received from at least one other device board by means of at least one transport module, wherein a transport module contains solely TDM-channels from another device board, and control means adapted to cause storage of the content of a transport module received from another device board in a corresponding receiving buffer and transferring the TDM-channels in the receiving buffer to at least one of the output ports for transmission of the TDM-channels from the transmitting section in TDM-frames, wherein transmission of a frame takes place when all TDM-channels to be included in the frame have been received in the transmitting section.
The present invention provides a node that is flexible and able to through-connect TDM-channels of different sizes simultaneously.
The present invention provides a node that is able to through-connect TDM-channels with a low and short delay simultaneously together with other types of traffic. For instance, purely ATM-cells can be put through the same node.
The invention also provides an inexpensive node, insomuch that the node is able to through-connect traffic that arrives at and departs from the node in transport modules, while, at the same time, enabling traffic to be through-connected that arrives at and departs from the node in TDM-frames. This is particularly advantageous when a node that through-connects traffic by means of transport modules already exists and it is desired to also use this node for through-coupling TDM-frames.
The present invention provides a node that through-connects TDM-channels with a short and constant delay.
By transport module is meant such devices as cells in ATM-switches or frames in nodes of the frame relay type. By device board is meant a module that is intended for connection to a node in a telecommunications system, such as, for instance, a circuit board having input ports and output ports that are connected to a switch core in an exchange. The device board may, for instance, be a circuit board connected to another circuit board in a magazine, via a backplane bus.
The invention will now be described in more detail with reference to preferred embodiments thereof and also with reference to the accompanying drawings.